The present invention relates to a tungsten sintered compact target used for forming a gate electrode or a wiring material in IC, LSI and the like by the sputtering method, and also relates to a tungsten film deposited using the above target.
In recent years, use of a material having lower electric resistance as an electrode material and a wiring material has been explored along with the higher integration in VLSIs. In view of this, highly-pure tungsten having low electric resistance, which is thermally and chemically stable, is used as an electrode material or a wiring material.
Electrode materials and wiring materials for VLSIs are generally manufactured by the sputtering method or the CVD method. The sputtering method is more widely used than the CVD method because the structure and operation of the sputtering equipment is relatively simple, and deposition by the sputtering method is easy and less expensive.
High purity and high density are required for a tungsten target. In recent years, a material having low electric resistance is further required for a film formed by depositing an electrode material and a wiring material for VLSI by sputtering using a tungsten target.
As described below, a tungsten sintered compact target can have improved purity and higher density, and solutions for achieving them have been disclosed. However, conditions required to lower electric resistance have been unknown, and thus studies and developments of that have not been undertaken.
When manufacturing a conventional tungsten sintered compact sputtering target, pressure sintering is commonly performed using a graphite die. For example, Patent Literatures 1, 2 and 3 as described below can be cited. In this case, C may inevitably be present in tungsten as an impurity. Further, Patent Literatures 4 and 5 describe schemes to achieve higher density although types of dies are not particularly specified therein.
These Patent Literatures are primarily intended to increase the density of a tungsten target, but not intended to reduce electric resistance.
In addition, Patent Literature 6 describes a tungsten sintered compact target having a reduced amount of C. More specifically it discloses a method of reducing specific resistance by decreasing a carbon content to 50 ppm or less (the smallest C content is 19 ppm as shown in Example therein).
Further, Patent Literature 7 discloses a technology for reducing a C content in a metal material in order to obtain a uniform film and to decrease the frequency of dust generation (the smallest C content is 10 ppm as shown in Example therein).
Moreover, Patent Literature 8 discloses a technology for reducing a C content to 30 ppm or less (the smallest C content is 6 ppm as shown in Example therein) in order to prepare a highly pure and highly densified tungsten sintered compact target.
Some of the above Patent Literatures envision a tungsten sintered compact target in which a carbon content is reduced to decrease specific resistance. However the reduction conditions have not been sufficient enough to produce a significant effect.    Patent Literature 1: Japanese Patent No. 3086447    Patent Literature 2: Japanese Patent No. 3721014    Patent Literature 3: WO02009/147900    Patent Literature 4: Japanese Patent Laid-Open No. 2005-171389    Patent Literature 5: Japanese Patent Laid-Open No. 2007-314883    Patent Literature 6: Japanese Patent Laid-Open No. H05-093267    Patent Literature 7: Japanese Patent Laid-Open No. 2001-335923    Patent Literature 8: Japanese Patent Laid-Open No. H07-076771